Estimation of genotype effects for milk proteins with animal and sire transmitting ability models

The objective of this work was to estimate the contribution of milk protein genotype to production traits of Holstein cattle. Two approaches were employed. The first was based on an animal model analysis of milk records in which cows were genotyped for milk protein variants. The second approach was the analysis of PTA of sires in which the sires were genotyped for their milk protein variants. Results of the animal model analysis agreed qualitatively with previously published analyses of cow records, indicating only a minor contribution of milk protein genotype to production traits. Qualitative similarity was also found between the analysis of sire transmitting abilities and the animal model. Algebraic results suggested, however, that an indirect analysis of published sire transmitting abilities does not provide unbiased estimates of differences in milk protein genotypes. Although analysis of PTA is simple, only a direct analysis of genotyped cows with an animal model provides unbiased estimates of genotype differences.